1. Field of Invention
This invention is directed to a method and an apparatus to obtain balanced phase shift from a resonator supporting nonreciprocal wave propagation. As such, uniform phase shift results whose amplitude shows insignificant dependence on the derived angle in phase shift thereby eliminating the need for an amplifier.
2. Prior Art
Microwave and millimeter-wave (MMW) devices and systems are becoming increasingly important today for both defense and commercial applications. For example, in the collision avoidance industries, low-profile antennas are needed providing electronically steerable radiations to detect and identify obstacles and protrusions in front of a moving vehicle. Upon navigation the receiver antennas need to follow and track the motion of GPS (Global Positioning Systems) satellites so as to continuously monitor and update their positions. Also, there is a need to create radiation nulls along certain spatial directions for an antenna transmitter/receiver to warrant secure and covert communications. Other applications can be found in target searching/tracking radars, satellite communication systems, and TV program broadcasting antennas installed with a civilian jet carrier.
In a phased array system it is possible to include frequency-agile materials (varactors, ferroelectrics, and ferrites) together with amplifiers to tune and adjust the phase and amplitude of each individual element so as to compose and tailor the overall radiation into a desirable pattern. However, beam forming in this manner is costly; depending on the speed, frequency, and angle of steering, each phase-shifting element can cost as much as $10 0˜1,000, and in a system containing 10,000 elements, the cost of the antenna array system becomes formidable. Power dissipation is another consideration, since amplifiers are used following each of the phase shifting processes to compensate signal propagation loss, or insertion loss. To avoid overheating, water cooling is, therefore, often applied in a large phased array system.
A radiation beam can also be steered via mechanical means, as commonly observed for a traffic radar installed at the airports. However, steering in this manner is slow, suffering from potential mechanical breakdowns. To incorporate free rotation, the antenna take up considerable space and the shape of the antenna is not conformal. As such, it is unlikely to apply a mechanically rotating radar in a body moving at high speed.
Collision avoidance radars are popular these days installed with automotive ground vehicles and with airline jets. However, the current collision avoidance radars perform only the basic functions for target detection; these radars are not able to recognize a target, and hence they do not have the intelligence to handle targets of different kinds. In order to give the radar such intelligence, a steering radar is needed, performing image reconstruction based upon information collected from a steering beam. This requires an array of radiators whose phases can be controlled with accuracy in an economic manner. The prior art is not able to accomplish this purpose.
Conventionally, a phase shifter is obtained by incorporating a transmission line whose electric length, or electric permittivity and/or magnetic permeability, can be varied by applying a voltage, a current, or a bias magnetic field, as explained in FIG. 1 below. However, to obtain a large angle in phase shift a long line is needed, which translates into high cost and large volume. Also, insertion loss can be a serious problem if the phase shifter demands a long transmission line to operate. Otherwise, significant return loss will result, if the electric property of the transmission line has been changed appreciably due to the resultant change in line impedance. Even worse, in applications for a large phased array a large number of phase shifters is required, and there are problems such as how to integrate the phase shifters with the array system providing compatibility and uniformity with economy and size fit.